Posted by Enigma on January 20, 2000, enigma2112_ad_learn_dot_com
Oval valves won't work; valves have to spin in their seats. DOHC is more of a marketing gimmick than anything. In a street car, there's really no reason to have 4 valves per cylinder. The basic reasoning behind a DOHC engine is that you can flow a lot more without having to use huge valves. The bigger the valves, the more inertia they have & the more problems running at high RPM. Also it's easier to design a 4-valve head to burn the fuel mixture more completely, with the spark plug right in the middle of the head. Unfortunately the performance gains aren't worth the expense; 2-vlave systems properly engineered give just as good performance for much less.
Posted by Jordan Gartenhaus on January 17, 2000, gartenha_ad_u_dot_arizona_dot_edu
Okay, I know a good deal about DOHC, but just not why exactly it works. I know that DOHC stands for dual overhead cams. If you don't already know, cams are metalic rods with lobes along it which lay across the cylinder head. They control the lift and timing of valves in motors via rockers for example. Some other forms of valve timing are: single overhead cams, pushrod, overhead valve and so on. All use cams, they are simply different placements of the cams or use pushrods and such. I know some cars benefit from DOHC becuase it utilizes more space on the top of the cylinder head. One disadvantage to it is that produces more friction than a SOHC motor does. Hope that clears things up. Although, I still don't understand why 4 valves per cylinder is any more efficient at using all the space on a cylinder head when you can use 2 valves that are oval. ????????????????? Sincerely,Jordan Gartenhaus

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